Rf Unit-Pa Pcb Transmit Path - Codan NGT 2010 RF Technical & Service Manual

Drawings
ALTERNATIVE TEXT
NOTE
When the Tune command is activated, IC408 pin 7 (sheet 3) goes low. This switches off
V413 to allow the 456.5 kHz local oscillator carrier (453.5 kHz for LSB) to be passed to
V206 (sheet 2) via CAR INJ. V206 inserts carrier to the input transformer T202 of the
first Tx mixer IC103 (sheet 1).
At the same time, IC408 pin 5 (Tx MUTE) goes high and switches on V203 (sheet 2).
Thus, IC202/C and IC202/B open the noise gate V204, which stops the inserted carrier
from being loaded by the sideband filter Z201.
The carrier at the output of the second mixer IC102 (sheet 1) is at the frequency of the
selected channel (the SCF). This frequency is used for tuning automatic antennas.
RF unit—PA PCB transmit path
Gain control stage
Drawing
ALTERNATIVE TEXT
The RF input is passed to T200, which turns the RF drive into push-pull. This is applied
to the variable gain stage V200 and V201. The FETs V202 and V203 are used as variable
resistors depending on the ALC voltage applied to the gates.
If there is no power output at the antenna connector, 5 V of ALC voltage is applied to the
gates, so that the resistance is low and the gain is at maximum. As the output from the PA
increases to the power set point (100 W or 125 W), the ALC voltage drops, thus
increasing the resistance in the FETs, and so reducing the gain of V200 and V201, and
keeping the Tx output power at the set level (100 W or 125 W).
The overall gain of the PA is set to a constant value by R205 (PA GAIN).
Drawing 04-03369, or
ALTERNATIVE TEXT
Drawing
The RF input is passed to T200, which turns the RF drive into push-pull. This is applied
to the variable gain stage V200 and V201. The FETs V202 and V203 are used as variable
resistors depending on the ALC voltage applied to the gates.
If there is no power output at the antenna connector, 5 V of ALC voltage is applied to the
gates, so that the resistance is low and the gain is at maximum. As the output from the PA
increases to the power set point (100 W or 125 W), the ALC voltage drops, thus
increasing the resistance in the FETs, and so reducing the gain of V200 and V201, and
keeping the Tx output power at the set level (100 W or 125 W). V16 and V17 switch
between 100 W and 125 W. When V17 is on, the output power is 100 W. When V17 is
off, the output power is 125 W.
The overall gain of the PA is set to a constant value by R205 (PA GAIN).
NGT Transceiver System Technical Service Manual
04-03378 (sheet 3), 04-03378 (sheet 2)
If the PCB issue status is -06 or earlier, see drawings
04-03378 (sheet 2)
04-03169
04-03542
and 04-03378 (sheet 1)
and 04-03378 (sheet 1).
NGT—Technical description (2010)
04-03378 (sheet 3),
81